The present invention relates to an electromagnetic clutch device wherein drive torque is connected or disconnected between a pair of rotary members using a magnetic force.
Japanese Patent Application Laid-open No. 11-153157 discloses a power transfer device wherein an electromagnet is arranged to attract an armature to cause a clutch to generate a friction force to transfer drive power. An electromagnetic clutch, forming a part of such a power transfer device, allows magnetic field lines to be permeated through a yoke, a rotor, a friction clutch and an armature of the electromagnet depending on a value of electric current flowing through a coil of the electromagnet thereby forming a magnetic flux loop. To this end, attempts have heretofore been made to use material made of iron for the yoke, the rotor, the friction clutch and the armature of the electromagnet. In particular, material made of carbon steel has been generally used for the rotor of the electromagnetic clutch with a view to preventing a drop in permeability of the magnetic field lines.
However, with only attempt made in merely selecting material with favorable permeability of the magnetic field lines, issues arise with the occurrence of strength poverty of the electromagnetic clutch mounted to an associated peripheral member such as a stationary case or strength poverty of the electromagnetic clutch in delivering drive torque at a given rate. This causes limitations in designing the electromagnetic clutch in another application as a device.